A study revealed that exposure to traffic-related air pollution, particularly in early pregnancy, was associated with an increased preterm birth risk in women with asthma. According to Medpage Today, the study is among the first to examine the potential impact of air pollution exposure on preterm birth before conception and is also among the first to suggest early environmental exposure may be a stronger risk factor for preterm birth in asthmatic women. The researchers aimed to determine whether or not a critical window of exposure exists or if women with asthma have a greater environmental exposure risk than other women.

The researchers linked electronic medical records for 223,502 deliveries in the US with modified Community Multiscale Air Quality model outputs. The Medpage Today report indicates that exposure models accounted for weather and both temporal and spatial dispersion with multiple sites across the US over an 8-year period. The research team wrote that they examined a broad range of exposure windows because there is no consensus on which windows are most crucial for preterm delivery risk.

Logistic regression with generalized estimating equations was used to estimate the odds ratio and 95% CIs for preterm births on the basis of the interaction of maternal asthma and particulate matter, as indicated on the Medpage Today report. For each gestational week 23 to 26, exposures among women who delivered were compared with women who were still pregnant, and 3-month preconception, whole pregnancy, weeks 1 to 28, and the last 6 weeks of gestation averages were also evaluated.

The analysis revealed that preterm births occurred in 11.7% of singleton deliveries across the entire study population and 33.6% of these deliveries were early preterm births. Also, significant asthma interactions were sporadic before 30 weeks gestation but more common during weeks 34 to 36. The odds of giving birth prematurely were notably higher among women with asthma for CO and NOx exposure prior to conception and early in pregnancy.

Additional results showed that during the last 6 weeks of pregnancy, preterm birth risk linked with PM10 was higher among women with asthma and O3 exposure in gestation weeks 8-21 among asthmatic women was associated with lower risk of preterm birth.

Overall, the results of the study showed that both short- and long-term exposure to nitrogen oxides and carbon monoxide appeared to raise the risk for early delivery by up to almost 30%. In addition, the risk appeared to be greatest when exposures occurred just before conception as well as in the early weeks of pregnancy. Researcher Pauline Mendola, PhD, says, “Women with asthma had a higher risk for preterm birth, compared to women without asthma, when they were exposed to the same levels of air pollution. That is basically a new finding.”

Mendola adds that women with asthma who are pregnant or trying to become pregnant should try to limit air pollution exposure whenever possible. “There are already guidelines calling for people with asthma to avoid ambient exposure on bad air pollution days. This may be especially important for women with asthma who are pregnant or trying to become pregnant,” says Mendola.

Source: Medpage Today